What makes a high-performing house?
By Heather Chandler and Chris Briley
There are a lot of loosely defined terms used to describe how “green” a house is. Luckily some professionals in our industry have worked very hard to find ways to quantify this almost intangible quality, and in so doing, have generated new nomenclature that can often sound foreign to those outside the industry.
LEED, for example, refers to a certification given to a building by the U.S. Green Building Council as meeting certain criteria across different categories of sustainability (sustainable sites, water efficiency, energy and atmosphere, materials and resources, indoor environmental quality, and awareness and education). Buildings are awarded certifications that follow an Olympic medal system where a LEED Silver certification is good, Gold is very good, and Platinum is a very impressive building with excellent scores in all categories.
Another term used to describe high performing homes is Net Zero. This refers to the building’s energy consumption and means that the building produces as much energy as it consumes. This is achieved through the use of renewable energy systems, most likely in the form of photovoltaic solar panels. It is also very likely that the home’s energy demand has been reduced by increasing the building’s insulation, system performance, and air tightness values. If a home produces MORE than it uses, it is said to be Net Positive.
The term Passive House or Passivhaus (not to be confused with passive solar design which refers to a design strategy) is an international standard focusing on the building’s energy demand, or how much energy a house uses. A certified Passivhaus uses about 90% less energy than a typical codecompliant house, meaning in essence that it can be heated in the dead of winter with the same amount of energy a single hair dryer consumes, or about the same amount of heat given off by a small dinner party. Impressive indeed!
When a home is EnergyStar certified, a series of energy modeling, inspections, and testing provide the completed home with a score on the HERS (Home Energy Rating System) index. The U.S. Department of Energy has determined that a typical, code-compliant, well-built home has a HERS score of 100. So if you hear of a house having a score of 80, that home uses only 80% of the energy of the typical home. The lower the score, the less energy it consumes and the better it is. If a home has a score of 0, then it is a net zero home. A HERS score below zero, means the house is net positive.
ACH50 (Air Changes per Hour at 50 pascals of pressure) is a rating that references a building’s airtightness and is determined by performing a blower door test to simulate a 20 mph wind gusting on the outside of the house. The average home loses roughly 25% of its heat through the small cracks and flaws in its building envelope (around windows, doors, and at corners). A 2002 Wisconsin study
showed that the median ACH50 of homes for sale was 3.9 and for newly constructed homes it was 2.5. To get below
this number takes real effort and diligence in the builder’s methods and the designer’s detailing. To be a passive house, a building must have an ACH50 of 0.6!
Of course many homes do not seek certifications or third party verification, but they do implement many of the same strategies as those homes that do. Often their proof is evidenced in their low utility bills or in their ease of comfort on those brutal Maine winter nights. The homes featured on the following pages all address sustainability and deliver high performance as compared to a typical home. Whether they pursue certification or not, a “high performance home” is one that implements the same strategies: they reduce energy demand by insulating, air-sealing, choosing well-insulated climate appropriate windows, choosing efficient mechanical systems, balancing air ventilation (see page 31), choosing efficient fixtures and appliances, and incorporating renewable energy systems if possible.
Every home has an impact on our environment: some great and some slight; some negative, some positive. A high performing home is one that is leading the building industry in a positive direction.